I have a question conserning DNA methylationIn my book there is a question concerning that there is 2 different uses of methylationin eukaryotes and prokaryotes and that these different task should be explained how they differ

I know that in eukaryotic cells there is a function of methylation that changes the chromatin structurewhich makes the gene "silent" by compresse it harder.

In prokaryotic cells the methylation act as a DNA controll machanism so that foreign DNA will get degradedby the restriction enzyme in the cell by methylate the native DNA.

But i still dont understand how these two different type of processes should be compared to eachother

In regards to the prokaryotic methylation, it also work in reverse. When DNA is methylated, some restriction enzymes are unable to cut the DNA. What do you mean by how to compare them? Their both secondary modifications to DNA, for one.

DNA methylation has different hallmarks in eukaryotes compared to prokaryotes. For example, eukaroytes favour the methylation of C when it appears in combination preceding G, referred to as CpG (where the p refers to the phosphate link of course). Bacteria will easily methylate cytosine as well but also adenine, and the pattern for cytosines is not restricted to CpG nor is the pattern remotely similar for adenine (e.g. GATC is a frequently modified motif in bacterial DNA). The reason of course is they produce different enzymes with the necessary capabilities.One of the similarities between eukaryotes and prokaryotes is that when DNA is copied, the new strand is temporarily unmethylated; this allows the repair mechanisms to identify which of the copies is the new one, and so mutations introduced at this stage are repaired with a high level of accuracy (fidelilty). The most commonly cited reasons (aside from DNA repair which is good enough reason for most people!) for methylation deployment are different when one looks at the two kingdoms of life: in bacteria, bacterial viruses (bacteriophages, or phages) have unmethylated DNA, and so they are targeted for deletion by unmethylated-DNA-destroying enzymes (DNAses). Eukaryotes usually require the promoter regions to have methylated DNA to identify them to promoter binding enzymes as active. This patterning in promoter methylation transfers to the next generation when a cell divides, but is reset to nil in the zygote, thus allowing pluripotent capability which would obviously be damaging to a developed organism in most cases but prevents possibly useful development e.g. amputated limb regrowth. However this is a simplification: Bacteria use methylation for other reasons (e.g. origin of replication is heavily methylated), and so do Eukaryotes.